2.4.3 Osmosis Flashcards
All cells are surrounded by a cell membrane which is, what?
partially permeable
Osmosis allows water to, what?
move in and out of cells by osmosis
What is Osmosis
Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane
In doing this, water is moving down its concentration gradient
Because the cell membrane is partially permeable, what does that mean?
it allows small molecules (like water) through but not larger molecules (like solute molecules)
What type of water potential does Dilute Solution have
dilute solution has a high water potential
What type of water potential does a concentrated solution have
low water potential
(Exam Tip) Osmosis refers only to what?
the movement of water molecules, so if in an exam you are talking about the movement of water, make sure you mention osmosis as this will often earn you a mark
The best explanations to do with osmosis will refer to water potential.
As a result of Osmosis what happens to animal cells
Animal cells lose and gain water as a result of osmosis
In animal cells, the results of osmosis can be severe, why?
As animal cells do not have a supporting cell wall, the results of osmosis can be severe
If an animal cell is placed into a strong sugar solution(with a lower water potential than the cell) , what happens?
it will lose water by osmosis and become crenated (shriveled up)
If an animal cell is placed into distilled water (with a higher water potential than the cell) what will happen?
it will gain water by osmosis as it has no cell wall to create turgor pressure
It will continue to gain water until the cell membrane is stretched too far and it bursts
Why is it important that Osmosis is carefully controlled in organisms
It is important that osmosis is carefully controlled in organisms to avoid damage to cells through lysis
What is Lysis
the breaking down of the membrane of a cell
What is osmoregulation
The Homeostatic control of the water potential across membranes within the body
The human body is adapted to maintain the optimum, what?
osmotic balance
What process does the human body do to maintain the optimum osmotic balance
using processes such as sweating or increasing and decreasing urine concentration
as a result of osmosis, what do plants do
Plant cells lose or gain water as a result of osmosis
As plant cells have a supporting cell wall, what are they protected from?
they are protected from cell lysis
If a plant cell is placed into a strong sugar solution, what will happen?
it will lose water by osmosis
What happens to a plant cell if they lose water by osmosis
The vacuole gets smaller and the cell membrane shrivels away from the cell wall
It becomes flaccid or plasmolyzed (shrivelled up)
If a plant cell is placed into distilled water (with a higher water potential than the cell), what happens?
it will gain water by osmosis
When the plant cell gains water by osmosis what happens
The vacuole gets bigger, pushing the cell membrane against the cell wall
The plant cell is described as being turgid or as containing a high turgor pressure (the pressure of the cytoplasm pushing against the cell wall)
Water entering the cell by osmosis makes the cell, what?
makes the cell rigid and firm
Why is it important for water to enter the plant cell
to provide support and strength for the plant – making the plant stand upright with its leaves held out to catch sunlight
If plants do not receive enough water, what happens to it?
the cells cannot remain rigid and firm (turgid) and the plant wilts
In hypertonic solution red blood cells have:
Red Blood Cells have higher water potential than solution.
Net movement of water out
Shrivelled cells
In isotonic solution red blood cells are:
The water potential is equal between red blood cells and solution
No net movement of water
Normal Cells
In hypertonic solution red blood cells have:
Red blood cells have lower water potential than solution
Net movement of water in
Cells swell, may lyse (burst)
